A visible-light wireless communication system is a next-generation wireless communication technology in which digital signals are transmitted by controlling the light-emitting properties of an LED (light emitting device) and visible-light signals are received by using a PD (photodiode). In a visible-light wireless communication system, an LED may function not only as an indoor lighting device, but also as a transmitter for digital signals. Due to its inherent properties of the visible-light wireless communication system, its coverage area may be limited to a range that can be reached by the visible light, and the quality of the communication channel may be determined by the amount of visible light.
FIG. 1 schematically illustrates the structure of a conventional visible-light wireless communication system, where drawing (a) of FIG. 1 illustrates the structure of a visible-light transceiver, and drawing (b) of FIG. 1 illustrates the structure of a visible-light receiver.
To be more specific, the visible-light transceiver 110 may be composed of an LED 111 that emits visible light, an LED drive circuit 112 that controls the driving of the LED 111, a power source unit 113 that supplies power to the LED drive circuit 112, a signal modulator unit 114 that modulates digital signals inputted from the outside into visible-light signals, and a control unit 115 that controls the driving of the LED drive circuit in accordance with the modulated visible-light signals.
Also, the visible-light receiver 120 may be composed of a PD (121) that detects the on/off states of the visible light to receive the visible-light signals, and a signal demodulator unit 122 that demodulates the visible-light signals received via the PD 121 into digital signals.
An existing method of localizing a mobile terminal using visible-light wireless communication is to have multiple LEDs transmit visible-light signals, each including the ID of the respective LED, and to check the IDs in the visible-light signals received by the mobile terminal to measure the position of the mobile terminal. Although the existing localization method described above may have its advantages in terms of maintenance and costs in establishing the system, there may be the disadvantage of low localization accuracy.
Another method of localizing a mobile terminal using visible-light wireless communication is found in Xiaohan, et al., “Improved Indoor Location Estimation Using Fluorescent Light Communication System with a Nine-Channel Receiver,” which discloses a method of arranging multiple PDs in a circular formation and measuring the position of the mobile terminal by using the intensities and the incident angles of the visible light received from various angles. Although the existing localization method described above may provide higher localization accuracy compared to the existing method using the IDs of the LEDs, there may be the disadvantage of high costs associated with establishing the system.